@4068682302
You upgrade and the pay for the upgrade as noted in the answer to the original message. You do NOT file or re-file a tax return.
Did you read the answer to this message before you posted on this thread??
In TurboTax Free Edition, you can purchase PLUS to unlock your prior-year .tax file.
The exact instructions will vary depending on the status of your 2018 TurboTax Online return (select one):
